IB MYP 4-5 Biology-Physiology- Study Notes - New Syllabus
IB MYP 4-5 Biology-Physiology- Study Notes – New syllabus
IB MYP 4-5 Biology-Physiology- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Circulatory: Heart structure, blood vessels, role of hemoglobin.
- Respiratory: Gas exchange, spirometry experiments.
- Nervous: Reflex arcs, synapses, reaction time labs.
- Homeostasis: Thermoregulation, blood glucose control.
Circulatory: Heart structure, blood vessels, role of hemoglobin.
🔄 Why Do We Need a Circulatory System?
Your body has trillions of cells, and they all need:
- 🚚 Oxygen & nutrients delivered
- ♻️ Waste products (like CO₂) removed
🧠 Think of it like: The circulatory system = your body’s 24/7 delivery + garbage truck system!
❤️ Heart: The Central Pump
Basic Facts:
- Size: About the size of your fist
- Location: Between the lungs, slightly to the left
- Function: Pumps blood throughout the body
🫀 Structure of the Heart (4 Chambers)
| Chamber | Function |
|---|---|
| Right Atrium | Receives deoxygenated blood from body |
| Right Ventricle | Pumps it to lungs via pulmonary artery |
| Left Atrium | Receives oxygenated blood from lungs |
| Left Ventricle | Pumps it to body via aorta (strongest chamber) |
🛑 Valves (like tricuspid, bicuspid, semilunar) prevent backflow of blood
💡 Double Circulation: Blood passes through the heart twice per full cycle.
- Pulmonary circulation: heart → lungs → heart
Systemic circulation: heart → body → heart
🩸 Blood Vessels: Highways of the Body
| Type | Carries | Features | Example |
|---|---|---|---|
| Arteries | Blood away from the heart | Thick, elastic walls, high pressure | Aorta |
| Veins | Blood to the heart | Thin walls, valves, low pressure | Vena cava |
| Capillaries | Connect arteries & veins | One cell thick, allows exchange | Near every cell |
🧠 Memory Tip: Arteries = Away, Veins = Visit the heart
🧬 Hemoglobin: The Oxygen Carrier
📌 What is it?
- A protein in red blood cells
- Contains iron (Fe²⁺) which binds to oxygen
🩸 Role:
- Picks up oxygen in lungs
- Transports it to tissues
- Also helps carry CO₂ back to lungs
🧪 Formula:
(Hemoglobin + Oxygen ↔ Oxyhemoglobin)
Without it, you’d need ~5,000 liters of blood just to carry enough oxygen!
💡 Did You Know? People with anemia have low hemoglobin levels → tiredness due to reduced oxygen delivery.
✏️ Quick Revision Points
- Heart = 4 chambers, valves, and double circulation
- Arteries = away from heart, thick walls
- Veins = to heart, thin walls with valves
- Capillaries = 1 cell thick, site of exchange
- Hemoglobin = protein in RBCs that carries O₂ + some CO₂
Respiratory: Gas exchange, spirometry experiments.
🎯 Why Do We Need a Respiratory System?
Every single cell in your body needs oxygen (O₂) to release energy via respiration and it needs to get rid of carbon dioxide (CO₂), a toxic waste gas.
The respiratory system = your body’s gas exchange system
🫁 Gas Exchange: How Oxygen Enters and CO₂ Leaves
🌬️ Where does gas exchange happen?
In the alveoli tiny air sacs inside the lungs.
You have 300 million+ alveoli, giving a surface area of ~70 m².
🔁 What Happens During Gas Exchange?
| Gas | Moves from → to | How |
|---|---|---|
| Oxygen (O₂) | Alveoli → Blood (capillaries) | Diffusion |
| Carbon dioxide (CO₂) | Blood → Alveoli | Diffusion |
Gases move from high → low concentration
Lungs have moist, thin walls and are surrounded by capillaries
Alveoli provide a huge surface area for maximum diffusion
📦 Features of Alveoli (for efficient gas exchange):
| Feature | Function |
|---|---|
| Thin walls (1 cell thick) | Fast diffusion |
| Moist lining | Dissolves gases for diffusion |
| Large surface area | More room for exchange |
| Rich capillary network | Maintains concentration gradient |
🧪 Spirometry: Measuring Lung Function
🧰 What is spirometry?
A clinical test used to measure:
- Lung capacity
- Airflow rate
- How well someone can inhale and exhale
It helps diagnose conditions like asthma, COPD, or lung fibrosis
📊 Key Spirometry Values to Know:
| Term | Meaning |
|---|---|
| Tidal Volume (TV) | Normal air inhaled/exhaled at rest |
| Inspiratory Reserve Volume (IRV) | Extra air you can inhale after a normal breath |
| Expiratory Reserve Volume (ERV) | Extra air you can exhale after a normal breath |
| Vital Capacity (VC) | Max air exhaled after a deep breath |
| Residual Volume (RV) | Air that remains in lungs after full exhalation |
| Total Lung Capacity (TLC) | VC + RV (all the air your lungs can hold) |
🧪 Sample Spirometry Experiment (Simple Lab Setup):
- Student breathes into a spirometer (or a balloon if simplified)
- Volume of air exhaled is measured
- Values plotted on a spirometer trace (graph)
- Compare values to norms for age, gender, height
✏️ Summary:
- Gas exchange = O₂ in, CO₂ out (via diffusion in alveoli)
- Alveoli: Thin, moist, large surface area, surrounded by capillaries
- Spirometry = lab test for lung function
Nervous: Reflex arcs, synapses, reaction time labs
🧠 What Is the Nervous System?
Your nervous system is like the body’s Wi-Fi + control center. It:
- Picks up signals (stimuli) from the environment
- Processes them quickly
- Sends instructions to muscles/organs to react
⚡ Reflex Arcs: Fast, Automatic Responses
What’s a reflex?
A quick, involuntary response to a stimulus no thinking involved
🧪 Examples:
- Pulling your hand away from a hot pan
- Blinking when something comes at your eyes
🧩 Reflex Arc Pathway:
| Step | Structure Involved |
|---|---|
| 1️⃣ Stimulus detected | Receptor (e.g. skin) |
| 2️⃣ Message sent | Sensory neuron |
| 3️⃣ Processed | Spinal cord (relay neuron) |
| 4️⃣ Message sent back | Motor neuron |
| 5️⃣ Response | Effector (muscle or gland) acts |
🔗 Synapses: Where Neurons Communicate
A synapse is a tiny gap between two neurons (like a plug and socket).
What happens at a synapse?
- Electrical signal reaches end of neuron
- Neurotransmitters are released into the gap
- They diffuse across the gap
- Trigger an electrical signal in the next neuron
🧠 Key words to remember:
- Neurotransmitters = chemical messengers
- Synapse = ensures one-way signal only
Diffusion = slower but precise
💡 Common neurotransmitters:
Acetylcholine (muscle control), dopamine (pleasure/movement), serotonin (mood)
🧪 Reaction Time Lab (Classic School Experiment)
🎯 Goal: Measure how fast your nervous system responds
🧪 Ruler Drop Test:
- One person holds a ruler vertically
- Another places fingers at zero mark
- Ruler dropped unexpectedly
- Distance fallen noted and converted to reaction time
🧠 Equation: t = √(2d/g)
- d = distance ruler fell (in meters)
- g = acceleration due to gravity (9.8 m/s²)
t = reaction time (in seconds)
✏️ Quick Recap:
| Topic | Key Ideas |
|---|---|
| Reflex Arc | Fast, automatic path: receptor → sensory → relay → motor → effector |
| Synapse | Gap between neurons; uses neurotransmitters for one-way signal |
| Reaction Time | Measured using ruler drop, shows speed of neural response |
Drugs like caffeine or alcohol change synaptic transmission and affect reaction time.
Homeostasis: Thermoregulation, blood glucose control.
🧠 What Is Homeostasis?
Homeostasis = Maintaining a stable internal environment despite external changes.
Think of it like your body having an automatic thermostat and internal balancing system 🔄
🔥 Thermoregulation (Temperature Control)
Your body temperature needs to stay around 37°C. If it gets too high or low, serious problems can occur.
Controlled by: Hypothalamus in the brain (acts like a thermostat)
🌡️ If You’re Too Hot…
| Response | How it helps |
|---|---|
| Sweating 💧 | Evaporation removes heat |
| Vasodilation 🔴 | Skin vessels widen → heat lost |
| Hairs lie flat | Less insulation = more heat escapes |
❄️ If You’re Too Cold…
| Response | How it helps |
|---|---|
| Shivering ❄️ | Muscles contract → generate heat |
| Vasoconstriction 🔵 | Vessels narrow → heat conserved |
| Hairs stand up | Traps insulating air (like fur) |
💡 Did You Know? A fever is actually your body’s way to fight infection by raising body temperature 🔥
🍭 Blood Glucose Regulation
Cells need glucose for energy. Too much or too little is dangerous.
Normal level: ~90 mg/dL (≈ 5 mmol/L)
🔬 Controlled by the Pancreas:
| Hormone | Released when… | Action |
|---|---|---|
| Insulin | Blood sugar too high | Stimulates cells to absorb glucose + store in liver as glycogen |
| Glucagon | Blood sugar too low | Stimulates liver to break down glycogen → glucose |
Target organ: Liver
💉 Diabetes (When Homeostasis Fails)
| Type | Cause | Effect |
|---|---|---|
| Type 1 | Autoimmune → no insulin produced | Needs insulin injections |
| Type 2 | Body cells resist insulin | Managed with diet, exercise, meds |
🧠 Memory Trick: Insulin ↓ blood sugar | Glucagon ↑ blood sugar
✏️ Summary Table: Homeostasis Examples
| System | Variable Controlled | Hormone/Mechanism |
|---|---|---|
| Thermoregulation | Body temp | Sweating, blood flow, shivering |
| Blood glucose | Glucose levels | Insulin ↓, Glucagon ↑ |
✅ Key Pointers:
- Homeostasis = keeping internal balance
- Thermoregulation = behavioral + physiological mechanisms
- Glucose control = negative feedback loop